1. Field of the Invention
The present invention relates to a portable information communication terminal having a function of for detecting multiple paths over a wireless transmission line, a program for such function, and recording medium on which the program is recorded.
2. Description of Related Art
In the direct sequence spread spectrum (DS-SS) system, multiple paths over a wireless transmission line are detected. Received signals of the multiple paths are rake-combined so as to alleviate influence of fading due to the multiple paths and improve the communication quality. Thus, a function for accurately detecting multiple paths to be rake-combined is important for a receiving apparatus of the direct sequence spread spectrum wireless communication.
To detect multiple paths, correlating calculations for received signals and a reference signal are required. In addition, to improve the detection accuracy of multiple paths, the correlating calculations are performed several times, and thus obtained results are averaged in general. These calculating process takes a relatively large part in all the receiving process. Thus, it is important to minimize the number of times (operating time) for the averaging operation is performed so as to reduce the power consumption of the receiving apparatus.
A method for suppressing the number of times for the averaging operation by deciding the number of times for the averaging operation in accordance with output levels of a correlation device that performs the correlating calculations for the received signals and the reference signal is disclosed in a first and a second related art references. A third related art reference discloses a method for decreasing an operation time by omitting an unnecessary cumulative adding operation.
The first related art reference is Japanese Patent Laid-Open Publication No. 2002-26768, the second related art reference is Japanese Patent Laid-Open Publication No. 2001-267958, and the third related art reference is Japanese Patent Laid-Open Publication No. 2001-136101.
However, when the number of times for the averaging operation is decided in accordance with the output levels of the correlation device, the following problems will arise.
First, the outputs of the correlation device are complex correlation values. Thus, it is preferred to perform an averaging operation by a coherent adding operation. However, the averaging operation by the coherent adding operation is difficult. Thus, after the outputs of the correlation device are converted into power values or amplitude values, thus converted values are averaged. However, the measurement accuracy of levels obtained by that method is inferior to that obtained through the averaging operation by the coherent adding operation. Since the number of times for the averaging operation is decided in accordance with the inaccurate outputs of the correlation device, the number of times for the averaging operation cannot be accurately decided.
The output levels of the correlation device have to be decided in accordance with the past reception states, and should not be decided with the current reception state. Thus, the number of times for the averaging operation cannot be derived in accordance with the current reception state.
In the actual receiving apparatus, the number of fingers is limited. In other words, since the number of paths that are able to be assigned is limited, if the paths that exceed the limited number are detected, this means that unnecessary process is preformed. However, in the related art references, control for the number of times for the averaging operation is not carried out in accordance with the number of fingers that is able to be assigned. Thus, the methods according to the related art references are not effective.